The present invention relates to an electric power-assist system for a manually-operated vehicles, and more particularly, to an electric bicycle having a motor used for assisting the pedaling force.
An electric power-assist system for manually-operated vehicle is able to deliver power according to current efforts devoted by the vehicle operator. With this electric power-assist system, vehicle operator is able to achieve the same speed with less effort, as compared to the situation when the vehicle is purely human power driven. Thus the operator is able to operate the vehicle in a more efficient way.
Currently, the electric power-assist system is implemented on a vehicle, such as shown in FIG. 1 of US2004/0206563A1, which takes an electric bicycle as an example. Pedaling force is sensed by torque sensor 11, which converts this force information to a signal. This signal is processed by units 19, 21 and 22, which decide how much PWM to output to motor driving block 14. Block 14 then controls the motor 13, which contains an encoder 16 that senses the rotation speed of the motor. Information from 16 is feedback to unit 19 via speed calculating blocks 17 and 18. Therefore the speed is regulated.
However, use of torque sensor bears a high cost, and leads a higher price of vehicles. Another existing method of implementing the electric power-assist system employs the “Hall sensor”—where the Hall sensor is used to sense the vehicle speed to be more than a certain threshold and then a fixed current is commanded in the motor. This method does not have advance feature of controlling the motor power output proportional to the human power input. Hence there will be a problem of unequal power output from the motor, resulting in insufficient assisting power from the motor during high speed or too much assisting power from the motor during low speed.
Therefore, a need arises such that the cost is brought down while advance feature of adapting assist power to human power effort is implemented.